Meat tenderness is an important issue in production of beef cattle, because it has a major impact on consumer's satisfaction. Consumers consider tenderness to be the single most important component of meat quality (Miller, (1992) Beef Today 8:40). The physiological change in muscle structure leading to increased tenderness during the postmortem period is complex (Koohmaraie, M. (1994) Meat Sci. 36: 93). The calpain/calpastatin system is an endogenous, calcium-dependent proteinase system, theorized to mediate the proteolysis of key myofibrillar proteins during postmortem storage of carcass and cuts of meat at refrigerated temperatures. Calpain is involved in the breakdown of myofibril protein, which is closely related to meat tenderness (Wheeler and Koohmaraie, 1994). Calpastatin inhibits μ- and m-calpain activity and, therefore, regulates postmortem proteolysis in part.
Many known non-genetic sources of variation may affect postmortem meat tenderization, including, for instance, the age of the cattle, deeding management, degree of stress prior to slaughter, and postmortem aging time (Tatum et al. 2000). However, approximately 30% of the variation in tenderness of meat can be explained by additive gene effects within a single breed (Koch et al. (1982) J. Anim. Sci. 1319-1329), which is greater than variation found among breeds (Wheeler et al. (1996) J. Anim. Sci. 74: 1023-1035).
An increase in postmortem calpastatin activity has been correlated to reduced meat tenderness (e.g., Koohmaraie et al. 1995 in: Ouali et al. (eds.) Expression of Muscle Proteinases and Regulation of Protein Degradation as Related to Meat Quality. Audet Tijdschrifren b.v., Nijmegen, The Netherlands pp 395-412; Pingle et al. 1997). The calpastatin (CAST) gene, mapped to bovine chromosome 7 (Bishop et al., J Anim Sci. 1993 August; 71(8):2277), is considered a candidate gene for beef tenderness. Initial studies, however, did not find significant association of CAST polymorphisms with tenderness. For instance, Lonergan et al. (1995) (J. Anim. Sci. 73: 3608-3612) did not find a significant association of restriction fragment length polymorphisms in the CAST gene with calpastatin activity or tenderness in crossbred offspring of sires from eight breeds. Chung et al. (1999) (J. Anim. Sci. 77 (Suppl 1): 31) investigated the association of PCR single strand conformation polymorphisms in the CAST gene with calapastatin activity, Warner-Bratzler shear force and myofibril fragmentation index in forty-seven purebred Angus bulls and concluded that the polymorphisms were not useful for prediction of calpastatin activity, myofibril fragmentation index or meat tenderness.
More recently two genetic tests for meat tenderness in beef have become available. The TenderGENE™ test (Merial Limited) is based on two markers (polymorphisms) in the Calpain gene. The GeneStar® Tenderness 2 (Genetic Solutions) is based on a marker in the CAST gene and one marker in the Calpain gene.
“Body condition” as understood in the livestock industry is the state of development of an animal as a function of frame type or size, and overall health and, in the case of non-poultry animals, the amount of intramuscular fat and back fat exhibited by an animal. The body condition of animals is a determinant of market readiness in commercial livestock breeding, feeding and finishing operations. Body condition is typically determined subjectively and through experienced visual appraisal of live animals. The fat deposition, or the amount of intramuscular fat and back fat on a non-poultry animal carcass, is important to industry participants because carcasses exhibiting desired amounts and proportions of such fats can often be sold for higher prices than carcasses that exhibit different amounts and proportions of fat. Furthermore, the desired carcass fat deposition often varies among different markets and buyers with time within single markets and among particular buyers in response to public demand trends with respect to desired fat and marbling in meats. Predictable and consistent body weight or carcass characteristics are also preferred.
Presently, cattle entering a feedlot are divided into groups according to estimated age, frame size, breed, weight, and so forth. By making such a division, the feedlot owner is attempting to group the animals so that a group can be penned together, fed the same diet and slaughtered at the same time. Weight and visual cues are one means possible to sort cattle for feedlot grouping.
The greater the production expectations, the greater the price realized by the feed operator. Regardless of the particular market preference at a given time, the feed lot operator will be trying to tailor his animals to meet some similar standard that will cause a meat packer or commercial purchaser to pay the highest price in accordance with currently prevailing market preferences.
While the cost of acquiring each animal in a group can vary somewhat, the feedlot operator's costs would be the same for each animal in a group since they would have access to the same amount of feed and occupy space in the feedlot for the same amount of time (not considering health costs due to sickness). Thus, the price reductions for animals falling outside the desirable range fall directly to the feedlot operator's bottom line, resulting in reduced profits. One way to reduce costs and increase profits is to minimize the time an animal spends at the feedlot, thereby reducing feed costs. Thus, longer residence times are usually only profitable if the result is an animal with a more profitable grade. The capability of predicting when an animal is ready for a market is also desirable.
There remains a need for methods that allow relatively easy and more efficient selection and breeding of farm animals with an advantage for an inheritable trait of growth rate, body weight, carcass merit, feed intake and milk yield and composition. The economic benefits of the use of genetic markers that are associated with specific economically important traits (especially traits with low heritability) in livestock through marker-assisted selection are significant.
Polymorphisms in the coding regions of the leptin gene in cattle have been associated with milk yield and composition (Liefers et al. (2002) J. Dairy Sci. 85: 1633-1638; Buchanan et al (2003) Dairy Sci. 86: 3164-3166), feed intake (Liefers et al. (2002); Lagonigro et al. (2003) Anim. Genet. 34: 371-374), and body fat (Buchanan et al. (2002) Genet. Sel Evol. 34: 105-116; Lagonigro et al., Anim Genet. 2003 October; 34(5):371-4. However, polymorphisms located in the promoter region of the leptin gene (i.e. the region of the gene that regulates the level of leptin expression through its associated enhancer and silencer elements) may have a stronger effect on the regulation of these economically important traits, and therefore be of greater predictive value.
Other SNPs identified with phenotypes of interest to the animal breeder or rearer are, for example, within the m-calpain (CAPN1) gene (Juszczuk-Kubiak et al. (2004) J. Appl. Genet. 45: 457-460. An SNP in the DGAT1 gene affects milk yield and composition (Grisar et al. (2004) Proc. Natl. Acad. Sci. U.S.A. 101: 2398-2403; Thaller et al. (2003) Anim. Genet. 34: 354-357; Kuhn et al. (2004) Genetics 167: 1873-1881). SNPs in the growth hormone receptor gene GHR may have significant effects on milk yield in particular breeds of cattle (Spelman et al. (2002) J. Dairy Sci. 85: 3514-3517; Blott et al. (2003) Genetics 163: 253-266).
Because of these deficiencies and others inherent in the prior art, it is still advantageous to provide further SNPs that may more accurately predict the meat quality phenotype of an animal and also a business method that provides for increased production efficiencies in livestock cattle, as well as providing access to various records of the animals and allows comparisons with expected or desired goals with regard to the quality and quantity of animals produced.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.